[Elecraft] Noise gen / Spectrogram--who invented?

[Ron D'Eau Claire]

Steve, GU3MBS:

I recall using Rhode & Schwarz test-sets for filter
alignment, also Tektronix tracking-generator and
spectrum analyzer combos.  Further back I recall
similar devices called wobbulators used for IFs.

- when was the technique of using wideband noise
   followed by audio or video spectrum analysis first
   described?

- ditto, for amateur radio applications?

-------------------------------

I can't cite the earliest documentation, but I know that filter-analysis
using broad-band noise and a spectrum analyzer combo was well known half a
century ago. In '62 I designed a production test station for Lenkurt
Electric using that process to align microwave filters. 

The difference is that those set-ups covered a good-sized workbench and
would have cost us over $50,000 in today's money.  

The power of the PC coupled with some clever code that we can buy for almost
"pocket change" has made techniques that were barely affordable to a large
corporation back then almost a basic part of any Ham workshop today. The
biggest short-coming of Spectrogram is the PC, too. That's what limits the
usable dynamic range of the measurements to about 60 dB. It still takes
better gear to do real stop-band attenuation measurements. 

The real advantage of Spectrogram is the visual display that is easily
interpreted.  It's "intuitive" by someone with a minimal understanding of
what's going on. That's exactly why we spent the money on the system I built
in the 60's. It needed to be operated correctly by factory alignment techs
with the least chance of error and  minimal 'training'. The same is true
today when someone wants to set up their K2 filters. 

For more exacting measurements over a larger dynamic range, I still rely on
a combination of either a tunable signal generator and sensitive broad-band
RF voltmeter or a wide-band noise source and a tunable RF voltmeter. Indeed,
when I build a filter for a project that falls within the K2's tuning range,
the K2 itself makes a great tunable RF voltmeter for such a setup. 

Ron AC7AC